From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Kzbnl-0001kz-Up for qemu-devel@nongnu.org; Mon, 10 Nov 2008 13:47:54 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Kzbnl-0001k6-7c for qemu-devel@nongnu.org; Mon, 10 Nov 2008 13:47:53 -0500 Received: from [199.232.76.173] (port=56415 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Kzbnl-0001jy-3s for qemu-devel@nongnu.org; Mon, 10 Nov 2008 13:47:53 -0500 Received: from yw-out-1718.google.com ([74.125.46.158]:12770) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1Kzbnk-0004CA-S1 for qemu-devel@nongnu.org; Mon, 10 Nov 2008 13:47:53 -0500 Received: by yw-out-1718.google.com with SMTP id 6so897815ywa.82 for ; Mon, 10 Nov 2008 10:47:52 -0800 (PST) Message-ID: <491881D4.5000203@codemonkey.ws> Date: Mon, 10 Nov 2008 12:47:48 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 0/4] VGA optimization References: <1226342253-8887-1-git-send-email-glommer@redhat.com> <49187FC8.60107@codemonkey.ws> In-Reply-To: <49187FC8.60107@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Anthony Liguori wrote: > Glauber Costa wrote: >> hey guys, >> > > I gave you some bad advice that I think is causing the breakage I'm > seeing now. I suggested that you simply do a lookup to find the slot > given a target_phys_addr_t but that isn't correct. Let me explain why. Except I'm completely backwards but at least consistently backwards :-) Regards, Anthony Liguori > ram_addr_t represents a guest physical address. From a ram_addr_t you > can get a target_phys_addr_t. Sometimes these are the same but they > aren't always. > > You can have multiple ram_addr_t's pointing to the same > target_phys_addr_t. This is ram aliasing and it happens for a variety > of reasons. In general, it's pretty expensive to map a ram_addr_t to > a target_phys_addr_t because, among other things, for a range of > (ram_addr_t, size_t), you may have many (target_phys_addr_t, size) > tuples that you have to deal with. > > vga_common_init() takes a target_phys_addr_t (well, it really takes an > unsigned long, but that's a bug). It takes this as an optimization. > It avoids having to do the conversion and ensures that it's one big > linear region. > > For dirty tracking, we have a bitmap indexed by target_phys_addr_t in > QEMU. This means that we can happily set dirty bits based on > target_phys_addr_t's. We don't have to worry about what ram_addr_t it > came from because they all map to the same bits. > > Since KVM uses a slot API, and that API is indexed in ram_addr_t's, we > need to enable dirty tracking on the ram_addr_t's. We don't have a > ram_addr_t in the VGA code. > > The solution is pretty simple. We need to keep track of the > ram_addr_t's in the VGA code and enable dirty tracking on the > appropriate ram_addr_ts. > > Regards, > > Anthony Liguori > >> I hope this is the last version (Of course, once this is merged, >> the optimizations of the optimization can start ;-) ) >> >> I split it in 4 patches. The first two ones are just moving >> things out of the way, and then #3 and #4 do the real thing. >> #3 kvm-side, #4 overall qemu. >> >> They merge most of the suggestion Anthony and Stefano's sent >> on last iteration. >> >> Hope you like it. >> >> >> >> >> >